Juan M. Toro and his colleagues at the Parc Cientific de Barcelona in Spain studied 16 rats exposed to sentences spoken in either Japanese or Dutch. The researchers trained the animals to push a lever in response to a specific sentence, and then played sentences in the other language as well. Rats that were trained to respond to Dutch did not push the lever after hearing Japanese and vice versa. Moreover, the creatures could differentiate between Japanese and Dutch sentences that they hadn't previously listened to. The rats' abilities were found to be somewhat limited, however: when different speakers were used for each sentence, the animals encountered more difficulty telling them apart. Nevertheless, Toro says "It was striking to find that rats can track certain information that seems to be so important in language development in humans."
Previously, the ability to distinguish one type of speech from another had been observed only in humans and tamarin monkeys. But just because rats share this skill with humans does not mean the animals utilize it in the same manner that we do. "Rats have not evolved the ability to track prosodic [rhythmic and intonational] clues for linguistic requirements," Toro explains. "It is more likely that they do it as a byproduct of other abilities that have some evolutionary relevance for them." The scientists present their findings in the January issue of the Journal of Experimental Psychology: Animal Behavior Processes.